Attention is now paid to polycarbonate/polylactic acid alloy with respect to reduction of environmental load because the polylactic acid is a resin derived from plant.
Polycarbonate has a low fluidity. When alloyed with polylactic acid, however, polycarbonate can be effectively imparted with high fluidity because of the high fluidity of the polylactic acid.
In view of the structure of polylactic acid, it is considered that polylactic acid alloyed with polycarbonate scarcely generates a harmful gas when combusted. Thus, polylactic acid is a resin which is expected to be utilized in the field of office automation equipment and home electric appliances which require a flame retardancy standard.
Conventional polycarbonate/polyester alloy is lacking in fluidity though it has excellent heat resistance and chemical resistance. Thus, for the purpose of imparting high fluidity to polycarbonate, some measures such as alloying with a styrene-based resin and addition of a plasticizer are generally taken (for example, Patent Document 1).
A polycarbonate/polylactic acid alloy having pearl-like gloss and excellent fluidity and thermal and mechanical properties is known but there remains a room for improving the impact strength thereof (for example, Patent Document 2).
A polycarbonate/polyester alloy is generally lacking in impact resistance. Conventional alloying technology only provides an Izod impact strength of several kJ/m2.
Therefore, it is necessary to further improve the impact resistance particularly in the field of automobiles which require excellent impact characteristics.
For the purpose of improving impact resistance, it is generally known to increase the interfacial strength of an alloy by improving the compatibility of a polymer alloy.
For example, a bisphenol A-type epoxy resin is used as a compatibilizer for polycarbonate/polyamide-polyether block copolymer (for example, Patent Document 3).
Further, an epoxy-modified styrene-butadiene-styrene copolymer (SBS) and a terpene-phenol resin are used as a compatibilizer for polycarbonate/styrene-type resin composition (for example, Patent Document 4).
With regard to the above-described systems, it is reported that the appearance defect is overcome and impact resistance is improved by controlling the conditions of interface between polycarbonate and a subsidiary material. However, no reports have been made with regard to polycarbonate/polylactic acid.
For the purpose of improving impact resistance of a polycarbonate alloy, addition of an acrylonitrile-butadiene-styrene block copolymer (ABS), an impact resisting polystyrene resin, etc. is also proposed (for example, Patent Document 5).
Any of the above-described systems, however, is lacking in fluidity. High fluidity is required for a thin wall article, which is a recent trend. Thus, there is a demand for developing new polycarbonate resin compositions.
For the purpose of imparting high fluidity to polycarbonate, a thought may occur to add a component which has better fluidity than polycarbonate and which is compatible with polycarbonate.
Polylactic acid which is a class of polyester has excellent affinity with polycarbonate. However, because polylactic acid has poor impact resistance, the range of its application is limited. For example, in the field of automobiles, an improvement of impact resistance is essential.
[Patent Document 1] Japanese Examined Patent Publication No. H07-068455
[Patent Document 2] Japanese Unexamined Patent Publication No. H07-109413
[Patent Document 3] Japanese Unexamined Patent Publication No. H07-026131
[Patent Document 4] Japanese Unexamined Patent Publication No. 2000-143912
[Patent Document 5] Japanese a Unexamined Patent Publication No. 2000-169692